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"Fast Path With Bail-Out" Technique for Virtual Memory Systems

IP.com Disclosure Number: IPCOM000061349D
Original Publication Date: 1986-Jul-01
Included in the Prior Art Database: 2005-Mar-09
Document File: 1 page(s) / 13K

Publishing Venue

IBM

Related People

Lang, TG: AUTHOR [+2]

Abstract

In a virtual memory-based operating system, the parameters for system function calls may reside in pageable virtual memory. A method is described to permit the operating system to process these functions, even if the virtual memory containing the parameters is not currently paged into real memory. The operating system of a Virtual Resource Manager (VRM) needs to support functions for virtual machine operating systems, such as loading segment registers and updating the virtual machine program status. These functions have input parameters which may reside in paged-out virtual memory. Also, these functions are heavily used, so they must execute as rapidly as possible to ensure acceptable performance of the virtual system.

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"Fast Path With Bail-Out" Technique for Virtual Memory Systems

In a virtual memory-based operating system, the parameters for system function calls may reside in pageable virtual memory. A method is described to permit the operating system to process these functions, even if the virtual memory containing the parameters is not currently paged into real memory. The operating system of a Virtual Resource Manager (VRM) needs to support functions for virtual machine operating systems, such as loading segment registers and updating the virtual machine program status. These functions have input parameters which may reside in paged-out virtual memory. Also, these functions are heavily used, so they must execute as rapidly as possible to ensure acceptable performance of the virtual system. The easiest solution is to simply read the memory containing the parameters and allow the demand paging support provided by the hardware and the virtual memory manager of the VRM to bring the data into real memory, allowing the operation to proceed. A problem with this is that the VRM must load a segment register to allow its programs and data to be accessed in virtual memory, and the segment register chosen for this purpose may conflict with the segment register needed to access the data. A solution to this problem is to implement the function with virtual memory translation turned off, so that the VRM does not need any segment registers for itself. However, if this is done, then the demand paging facilities cannot be used since they require translation to be turned on. In accordance with the new method, the Load Segment Register (LSR) and Load Program Status (LPS) functions of the VRM are implemented with address translation turned off, for two reasons. First, a segment register doesn't have to be loaded to access VRM programs and data, so there is no conflict with the segment register being used to address the parameter d...